Control system for electric vehicles

ABSTRACT

When an electric vehicle is traveling downhill, experiencing regenerative braking, or otherwise forcing the vehicle motor to turn faster than the commanded motor torque, the vehicle motor produces electrical energy that can be used to recharge a vehicle battery. However, if the vehicle battery is already nearly or fully charged, the excess electrical energy produced may damage the battery. Control systems described herein may reduce and/or dispose of the excess energy by manipulating the motor flux (i.e., direct) current and quadrature current independently.

FIELD

This disclosure relates to systems and methods for managing energyrecover in regenerative braking systems for electric vehicles.

INTRODUCTION

When a self-balancing (or other) electric vehicle utilizing a permanentmagnet motor is in the process of stopping or being driven downhill, thesystem may be configured to inherently recover energy and oppose forwardmotion by causing the hub motor(s) to function as a generator, therebyconverting kinetic energy into a regenerating current (typicallydirected to the battery) and producing a braking torque. Thisregenerated current can be a benefit, e.g., when used to recharge abattery. However, the current can also be damaging, e.g., if the batteryis already at full capacity. Known vehicles attempt to resolve thispotentially damaging over-voltage situation by forcing the rider to slowdown below the regenerating threshold (which may, e.g., be 0.5 MPH), bydissipating current using resistor banks, or by suddenly shutting off. Abetter solution is needed to provide a better rider experience whilealso preventing damage to the battery.

SUMMARY

The present disclosure provides systems, apparatuses, and methodsrelating to control systems having over-voltage prevention features inregenerative energy situations. In some embodiments, a control systemfor an electric vehicle may include: a power supply; an electric motorcoupled to the power supply; and a motor controller having afield-oriented control (FOC) scheme configured to control the electricmotor by manipulating a direct current aligned with a rotating rotorflux angle and a quadrature current defined at ninety degrees from therotating rotor flux angle, wherein manipulation of the direct current isindependent of manipulation of the quadrature current, and the motorcontroller includes processing logic configured to: determine whether acounter electromotive force (CEMF) of the electric motor exceeds avoltage of the power supply by comparing a bus voltage of the powersupply to a voltage threshold; and in response to the bus voltage beinggreater than the voltage threshold, weakening a motor flux of theelectric motor and reducing the CEMF by automatically increasing thedirect current.

In some embodiments, an electric vehicle may include: one or morewheels; an electric hub motor coupled to a power supply and configuredto drive the one or more wheels; a motor controller having afield-oriented control (FOC) scheme configured to control the electrichub motor by manipulating a direct current aligned with a rotating rotorflux angle and a quadrature current defined at ninety degrees from therotating rotor flux angle, wherein manipulation of the direct current isindependent of manipulation of the quadrature current, and the motorcontroller includes processing logic configured to: determine whether acounter electromotive force (CEMF) of the electric motor exceeds avoltage of the power supply by comparing a bus voltage of the powersupply to a voltage threshold; and in response to the bus voltage beinggreater than the voltage threshold, weakening a motor flux of theelectric motor and reducing the CEMF by automatically increasing thedirect current.

In some embodiments, a method for preventing damage to a power supply ofan electric vehicle during regenerative braking may include: controllingan electric motor using a motor controller having a field-orientedcontrol (FOC) scheme configured to control the electric motor bymanipulating a direct current aligned with a rotating rotor flux angleand a quadrature current defined at ninety degrees from the rotatingrotor flux angle, wherein manipulation of the direct current isindependent of manipulation of the quadrature current; using processinglogic of the motor controller to determine whether a counterelectromotive force (CEMF) of the electric motor exceeds a voltage ofthe power supply; and in response to the CEMF of the electric motorexceeding the voltage of the power supply, weakening a motor flux of theelectric motor and reducing the CEMF by automatically increasing thedirect current.

Features, functions, and advantages may be achieved independently invarious embodiments of the present disclosure, or may be combined in yetother embodiments, further details of which can be seen with referenceto the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an illustrative one-wheeled electricvehicle suitable for use with aspects of the present disclosure.

FIG. 2 is an isometric view of another illustrative one-wheeled electricvehicle showing a rider mounted thereon.

FIG. 3 is a bottom oblique isometric view of the vehicle of FIG. 2.

FIG. 4 is a schematic diagram of illustrative electrical controls of thevehicles of FIGS. 1-3.

FIG. 5 is a schematic diagram of an illustrative Field Oriented Control(FOC) system in accordance with aspects of the present disclosure.

FIG. 6 is a schematic diagram depicting an illustrative three-axisreference system used by the FOC system of FIG. 5.

FIG. 7 is a schematic diagram depicting the variation over time of threeillustrative currents associated with the reference system of FIG. 6.

FIG. 8 is a schematic diagram depicting an illustrative two-axisreference system used by the FOC system of FIG. 5.

FIG. 9 is a schematic diagram depicting the variation with time of twoillustrative currents associated with the reference system of FIG. 8.

FIG. 10 is a schematic diagram depicting an illustrative rotatingtwo-axis reference system used by the FOC system of FIG. 5.

FIG. 11 is a schematic diagram depicting the variation with time of twoillustrative currents associated with the reference system of FIG. 10.

FIG. 12 is a flowchart depicting steps of an illustrative method forlimiting over-voltage conditions in an electric vehicle using an FOCsystem according to the present teachings.

FIG. 13 is a flowchart depicting steps of another illustrative methodfor limiting over-voltage conditions in an electric vehicle using theFOC system according to the present teachings.

DESCRIPTION

Various aspects and examples of a control system for electric vehicleshaving over-voltage prevention features in regenerative energysituations, as well as related methods, are described below andillustrated in the associated drawings. Unless otherwise specified, adisclosed control system and/or its various components may, but are notrequired to, contain at least one of the structure, components,functionality, and/or variations described, illustrated, and/orincorporated herein. Furthermore, unless specifically excluded, theprocess steps, structures, components, functionalities, and/orvariations described, illustrated, and/or incorporated herein inconnection with the present teachings may be included in other similardevices and methods, including being interchangeable between disclosedembodiments. The following description of various examples is merelyillustrative in nature and is in no way intended to limit thedisclosure, its application, or uses. Additionally, the advantagesprovided by the examples and embodiments described below areillustrative in nature and not all examples and embodiments provide thesame advantages or the same degree of advantages.

DEFINITIONS

The following definitions apply herein, unless otherwise indicated.

“Substantially” means to be more-or-less conforming to the particulardimension, range, shape, concept, or other aspect modified by the term,such that a feature or component need not conform exactly. For example,a “substantially cylindrical” object means that the object resembles acylinder, but may have one or more deviations from a true cylinder.

“Comprising,” “including,” and “having” (and conjugations thereof) areused interchangeably to mean including but not necessarily limited to,and are open-ended terms not intended to exclude additional, unrecitedelements or method steps.

Terms such as “first”, “second”, and “third” are used to distinguish oridentify various members of a group, or the like, and are not intendedto show serial or numerical limitation.

“Coupled” means connected, either permanently or releasably, whetherdirectly or indirectly through intervening components, and is notnecessarily limited to physical connection(s).

“AKA” means “also known as,” and may be used to indicate an alternativeor corresponding term for a given element or elements.

“Resilient” describes a material or structure configured to be deformedelastically under normal operating loads (e.g., when compressed) and toreturn to an original shape or position when unloaded.

“Rigid” describes a material or structure configured to be stiff,non-deformable, or substantially lacking in flexibility under normaloperating conditions.

The terms “inboard,” “outboard,” “forward,” “rearward,” and the like areintended to be understood in the context of a vehicle or host vehicle(if describing a component). For example, “outboard” may indicate arelative position that is laterally farther from the centerline of thevehicle, or a direction that is away from the vehicle centerline.Conversely, “inboard” may indicate a direction toward the centerline, ora relative position that is closer to the centerline. Similarly,“forward” means toward the front portion of the vehicle, and “aft” meanstoward the rear of the vehicle. In the absence of a host vehicle, thesame directional terms may be used as if the vehicle were present. Forexample, even when viewed in isolation, a device may have a “forward”edge, based on the fact that the device would be installed with the edgein question facing in the direction of the front portion of the hostvehicle.

“Processing logic” may include any suitable device or hardwareconfigured to process data by performing one or more logical and/orarithmetic operations (e.g., executing coded instructions). For example,processing logic may include one or more processors (e.g., centralprocessing units (CPUs) and/or graphics processing units (GPUs)),microprocessors, clusters of processing cores, FPGAs (field-programmablegate arrays), artificial intelligence (AI) accelerators, digital signalprocessors (DSPs), and/or any other suitable combination of logichardware.

OVERVIEW

In general, an electrical motor can function either as a motor or as agenerator. When functioning as a motor, the device receives electricalpower from a power source (e.g., a battery) and converts the electricalpower to a torque, thereby spinning a rotor. Spinning the rotor alsocauses a counter electromotive force (CEMF) (also referred to as backEMF), which opposes the voltage applied by the power source (e.g.,battery). In general, increasing the applied voltage speeds up therotor. As rotor speed increases, CEMF also increases, thereby creating agreater opposing effect. Conversely, when functioning as a generator,the device receives mechanical power from a mechanical (e.g., rotating)power source, and converts the kinetic energy into electrical power. Inthis case, spinning the rotor also causes a counter torque or counterforce, which acts to oppose the source of mechanical power. In general,this counter torque makes it increasingly more difficult to increase therotor speed.

During normal motoring operation, electrical motors exhibit both motorand generator characteristics. The production of CEMF is in effect agenerating activity. However, the CEMF is typically lower than the powersource voltage, and, as long as this is the case, the motor continues toact as a load (i.e., a motor). In some instances, the CEMF may exceedthe power source voltage, causing the generator function to dominate. Inthese situations, the device produces electrical energy that can be usedor recaptured. In a regenerative braking system, the energy isrecaptured by feeding it into the power source (e.g., recharging thebattery).

Situations that result in this sort of regenerative activity orrecapture of energy include when an electric vehicle is traveling down ahill or otherwise forcing the motor to turn faster than the commandedmotor torque. When the motor turns fast enough that the CEMF exceeds thebattery voltage, current will flow out of the motor and into thebattery. At the same time, because the motor is now acting as agenerator, a counter torque is produced. This counter torque functionsas a brake on the vehicle.

Although regenerative braking of the type just described is a usefulfeature, it may in some situations be harmful or undesirable. Forexample, the vehicle's battery may already be nearly or fully charged.An over-voltage condition can damage the system, so when the battery isalready nearly or fully charged, standard regenerative braking isundesirable.

Control systems described herein employ a technique to reduce and/ordispose of this excess energy to prevent over-voltage damage when thevehicle is regenerating power. Specifically, energy is redirected usinga version of Field Oriented Control (FOC) (also referred to as VectorControl). When the vehicle is operating, a flux current (AKA directcurrent) is defined having a vector aligned with the rotating rotor fluxangle, and a quadrature current is defined at 90 degrees from therotating rotor flux angle. Systems of the present disclosure redirectenergy by manipulating the flux current independently from thequadrature current.

During normal operations, quadrature current is controlled in accordancewith desired motor torque, while flux current is typically set to zero,e.g., so as not to counteract the motor's permanent magnets. However, ina possible over-voltage situation, systems of the present disclosure areconfigured to automatically weaken the motor flux by adjusting the fluxcurrent. This has two effects. First, the current used to weaken theflux is itself a load on the system, therefore opposing batteryregeneration. Second, by weakening the flux, the CEMF is reduced, suchthat the CEMF does not exceed the battery voltage as much. Accordingly,the motor generates less of the current that would otherwise be fed intothe battery.

Aspects of the present control systems may be embodied as a computermethod, computer system, or computer program product. Accordingly,aspects of the present control systems may include processing logic andmay take the form of an entirely hardware embodiment, an entirelysoftware embodiment (including firmware, resident software, micro-code,and the like), or an embodiment combining software and hardware aspects,all of which may generally be referred to herein as a “circuit,”“module,” or “system.” Furthermore, aspects of the present controlsystems may take the form of a computer program product embodied in acomputer-readable medium (or media) having computer-readable programcode/instructions embodied thereon.

Any combination of computer-readable media may be utilized.Computer-readable media can be a computer-readable signal medium and/ora computer-readable storage medium. A computer-readable storage mediummay include an electronic, magnetic, optical, electromagnetic, infrared,and/or semiconductor system, apparatus, or device, or any suitablecombination of these. More specific examples of a computer-readablestorage medium may include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, and/or any suitable combination ofthese and/or the like. In the context of this disclosure, acomputer-readable storage medium may include any suitablenon-transitory, tangible medium that can contain or store a program foruse by or in connection with an instruction execution system, apparatus,or device.

A computer-readable signal medium may include a propagated data signalwith computer-readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, and/or any suitable combination thereof. Acomputer-readable signal medium may include any computer-readable mediumthat is not a computer-readable storage medium and that is capable ofcommunicating, propagating, or transporting a program for use by or inconnection with an instruction execution system, apparatus, or device.

Program code embodied on a computer-readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, and/or the like, and/or any suitablecombination of these.

Computer program code for carrying out operations for aspects of thepresent control systems may be written in one or any combination ofprogramming languages, including an object-oriented programming languagesuch as Java, C++, and/or the like, and conventional proceduralprogramming languages, such as C. Mobile apps may be developed using anysuitable language, including those previously mentioned, as well asObjective-C, Swift, C#, HTML5, and the like. The program code mayexecute entirely on a user's computer, partly on the user's computer, asa stand-alone software package, partly on the user's computer and partlyon a remote computer, or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), and/or the connection may be made toan external computer (for example, through the Internet using anInternet Service Provider).

Aspects of the present control systems are described below withreference to flowchart illustrations and/or block diagrams of methods,apparatuses, systems, and/or computer program products. Each blockand/or combination of blocks in a flowchart and/or block diagram may beimplemented by computer program instructions. The computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block(s).In some examples, machine-readable instructions may be programmed onto aprogrammable logic device, such as a field programmable gate array(FPGA).

These computer program instructions can also be stored in acomputer-readable medium that can direct a computer, other programmabledata processing apparatus, and/or other device to function in aparticular manner, such that the instructions stored in thecomputer-readable medium produce an article of manufacture includinginstructions which implement the function/act specified in the flowchartand/or block diagram block(s).

The computer program instructions can also be loaded onto a computer,other programmable data processing apparatus, and/or other device tocause a series of operational steps to be performed on the device toproduce a computer-implemented process such that the instructions whichexecute on the computer or other programmable apparatus provideprocesses for implementing the functions/acts specified in the flowchartand/or block diagram block(s).

Any flowchart and/or block diagram in the drawings is intended toillustrate the architecture, functionality, and/or operation of possibleimplementations of systems, methods, and computer program productsaccording to aspects of the present control systems. In this regard,each block may represent a module, segment, or portion of code, whichcomprises one or more executable instructions for implementing thespecified logical function(s). In some implementations, the functionsnoted in the block may occur out of the order noted in the drawings. Forexample, two blocks shown in succession may, in fact, be executedsubstantially concurrently, or the blocks may sometimes be executed inthe reverse order, depending upon the functionality involved. Each blockand/or combination of blocks may be implemented by special purposehardware-based systems (or combinations of special purpose hardware andcomputer instructions) that perform the specified functions or acts.

EXAMPLES, COMPONENTS, AND ALTERNATIVES

The following sections describe selected aspects of exemplary electricvehicles and motor control systems therefor, as well as related systemsand/or methods. The examples in these sections are intended forillustration and should not be interpreted as limiting the entire scopeof the present disclosure. Each section may include one or more distinctembodiments or examples, and/or contextual or related information,function, and/or structure.

A. Illustrative Vehicle

FIG. 1 depicts an illustrative electric vehicle 10 that may be suitablefor use with an FOC-based over-voltage protection system in accordancewith aspects of the present disclosure. Other electric vehicles may alsobe suitable for the energy recovery control systems described herein.

Vehicle 10 is a one-wheeled, self-stabilizing skateboard substantiallysimilar to the electric vehicles described in U.S. Pat. No. 9,101,817(the '817 patent), the entirety of which is hereby incorporated hereinfor all purposes. Accordingly, vehicle 10 includes a board 12 having aframe 14 supporting a first deck portion 16 and a second deck portion18. Each deck portion 16, 18 is configured to receive a left or rightfoot of a rider oriented generally perpendicular to a direction oftravel of the board (see FIG. 2), said direction of travel generallyindicated at 20.

Vehicle 10 also includes a wheel assembly 22. Wheel assembly 22 includesa rotatable ground-contacting element 24 (e.g., a tire, wheel, orcontinuous track) disposed between and extending above the first andsecond deck portions 16, 18, and a hub motor 26 configured to rotateground-contacting element 24 to propel the vehicle. As shown in FIG. 1,vehicle 10 may include exactly one ground-contacting element.

Frame 14 may include any suitable structure configured to rigidlysupport the deck portions and to be coupled to an axle of the wheelassembly, such that the weight of a rider may be supported on tiltableboard 12 having a fulcrum at the wheel assembly axle. Frame 14 mayinclude one or more frame members 28, on which deck portions 16 and 18may be mounted, and which may further support additional elements andfeatures of the vehicle, such as a charging port 30, and end bumpers 32,34, as well as lighting assemblies, battery and electrical systems,electronics, controllers, and the like (see, e.g., FIGS. 4-11 andcorresponding description).

Deck portions 16 and 18 may include any suitable structures configuredto support the feet of a rider, such as non-skid surfaces, as well asvehicle-control features, such as a rider detection system. In someexamples, a rider detection system includes a strain gauge riderdetection system. Illustrative deck portions, including other suitablerider detection systems, are described in the '817 patent, as well as inU.S. patent application Ser. No. 14/934,024, the entirety of which ishereby included herein for all purposes.

A shaft 36 of an axle portion of hub motor 26 is coupled to frame 14, asshown in FIG. 1. For example, the shaft may be directly attached toframe 14, or may be coupled to the frame through a connection ormounting block 40 (also referred to as an axle mount). Shaft 36 may bebolted or otherwise affixed to mounting block 40, which in turn may bebolted or affixed to frame 14 (e.g., by bolts 42, 44). A through hole 46may be provided in frame 14 for access to the connector of shaft 36 toblock 40.

FIGS. 2-3 depict another example of a self-balancing electric vehiclesubstantially similar to vehicle 10, indicated at 100. Vehicle 100includes a board (or foot deck, or frame, or platform) 104 having anopening 108 for receiving a wheel assembly 112 between first and seconddeck portions (or footpads) 116, 120. First and second deck portions116, 120 may be of the same physical piece, or may be separate pieces.First and second deck portions 116, 120 may be included in board 104.First and second deck portions 116, 120 are each configured to support arider's foot. For example, first and second deck portions 116, 120 mayeach be configured to receive a left or a right foot of the rider.

Board/frame 104 may define a plane. First deck portion 116 is mounted toframe 104 and configured to support a first foot of the rider. Seconddeck portion 120 is mounted to frame 104 and configured to support asecond foot of the rider.

Wheel assembly 112 is disposed between first and second deck portions116, 120. First and second deck portions 116, 120 may be located onopposite sides of wheel assembly 112 with board 104 being dimensioned toapproximate a skateboard. In other embodiments, the board mayapproximate a longboard skateboard, snowboard, surfboard, or may beotherwise desirably dimensioned. In some examples, deck portions 116,120 of board 104 may be covered with non-slip material portions 124, 128(e.g., ‘grip tape’) to aid in rider control.

Wheel assembly 112 includes a ground-contacting element (e.g., a tire,wheel, or continuous track) 132. As shown, vehicle 100 includes exactlyone ground-contacting element 132, and the exactly one ground-contactingelement is disposed between first and second deck portions 116, 120.Ground-contacting element 132 is coupled to a motor assembly 136. Motorassembly 136 is mounted to board 104. Motor assembly 136 includes anaxle 140, which is coupled to board 104 by one or more axle mounts andone or more fasteners, such as a plurality of bolts. Motor assembly 136may be configured to rotate ground-contacting element 132 around (orabout) axle 140 to propel vehicle 100. For example, motor assembly 136may include an electric motor, such as a hub motor 144, configured torotate ground-contacting element 132 about axle 140 to propel vehicle100 along the ground.

Vehicle 100 has a pitch axis A1, a roll axis A2, and a yaw axis A3 (seeFIG. 2). Pitch axis A1 is the axis about which tire 132 is rotated bymotor assembly 136. For example, pitch axis A1 may pass through axle 140(e.g., pitch axis A1 may be parallel to and aligned with an elongatedirection of axle 140). Roll axis A2 is perpendicular to pitch axis A1,and may substantially extend in a direction in which vehicle 100 may bepropelled by motor assembly 136. For example, roll axis A2 may extend inan elongate direction of board 104. Yaw axis A3 is perpendicular topitch axis A1 and to roll axis A2. For example, yaw axis A3 may benormal to a plane defined by deck portions 116, 120, as shown in FIG. 2.

Wheel 132 may be mounted to frame 104 between deck portions 116, 120,and may extend above and below the plane defined by frame 104. Wheel 132may be configured to rotate about an axis (e.g., pitch axis A1) lying inthe plane. In addition, roll axis A2 may lie in the plane defined byframe 104. In some embodiments, the pitch and roll axes may define theplane.

Tire 132 may be wide enough in a heel-toe direction (e.g., in adirection parallel to pitch axis A1), so that the rider can balance inthe heel-toe direction using his or her own balance. Tire 132 may betubeless, or may be used with an inner tube. Tire 132 may be anon-pneumatic tire. For example, tire 132 may be “airless”, solid,and/or made of foam. Tire 132 may have a profile such that the rider canlean vehicle 100 over an edge of tire 132 (and/or pivot the board aboutroll axis A2 and/or yaw axis A3) through heel and/or toe pressure tocorner vehicle 100.

Hub motor 144 may be mounted within tire (or wheel) 132 and may beinternally geared or may be direct-drive. The use of a hub motor mayeliminate chains and belts, and may enable a form factor thatconsiderably improves maneuverability, weight distribution, andaesthetics. Mounting tire 132 onto hub motor 144 may be accomplished byeither a split-rim design that may use hub adapters, which may be boltedon to hub motor 144, or by casting a housing of the hub motor such thatit provides mounting flanges for a tire bead directly on the housing ofthe hub motor.

With continuing reference to FIGS. 2-3, a first skid pad 208 may beintegrated into (or connected to) a first end of board 104 proximalfirst deck portion 116, and a second skid pad 212 may be integrated into(or connected to) a second end of board 104 proximal second deck portion120. Skid pads 208, 212 may be replaceable and/or selectively removable.For example, the skid pads may include replaceable polymer parts orcomponents. In some embodiments, the skid pads may be configured toallow the rider to bring vehicle 100 to a stop in an angled orientation(e.g., by setting one end of the board against the ground after therider removes their foot from a rider detection device or switch, whichis described below in further detail). The respective skid pad may beworn by abrasion with the surface of the ground as that end of the boardis set against (or brought into contact with) the ground.

Vehicle 100 may include one or more side-skid pads configured to protectthe paint or other finish on board 104, and/or otherwise protect vehicle100 if, for example, vehicle 100 is flipped on its side and/or slidesalong the ground on its side. For example, the one or more side-skidpads may be removably connected to one or more opposing longitudinalsides of the board (e.g., extending substantially parallel to the rollaxis). FIG. 2 shows a first side-skid pad 216 connected to a firstlongitudinal side 104 a of board 104. In FIG. 3, side-skid pad 216 hasbeen removed from first longitudinal side 104 a. A second side-skid pad(not shown) may be similarly removably connected to a secondlongitudinal side 104 b (see FIG. 3) of board 104 opposite firstlongitudinal side 104 a. The side-skid pads may be incorporated into theelectric vehicle as one or more removable parts or components, and/ormay be or include replaceable polymer parts or components.

A removable connection of the skid pads and/or the side-skid pads to theboard may enable the rider (or other user) to selectively remove one ormore of these pads that become worn with abrasion, and/or replace theworn pad(s) with one or more replacement pads.

As shown in FIG. 3, vehicle 100 may include a handle 220. Handle 220 maybe disposed on an underside 104 c of board 104. Handle 220 may beintegrated into a housing or enclosure of one or more of the electricalcomponents.

In some embodiments, handle 220 may be operable between IN and OUTpositions. For example, handle 220 may be pivotally connected to board104, with the IN position corresponding to handle 220 substantiallyflush with underside 104 c of board 104, and the OUT positioncorresponding to handle 220 pivoted (or folded) away from underside 104such that handle 220 projects away from deck portion 120.

Vehicle 100 may include any suitable mechanism, device, or structure forreleasing handle 220 from the IN position. For example, vehicle 100 mayinclude a locking mechanism 224 that is configured to operate handle 220between a LOCKED state corresponding to handle 220 being prevented frommoving from the IN position to the OUT position, and an UNLOCKED statecorresponding to handle 220 being allowed to move from the IN positionto the OUT position. In some embodiments, the rider may press lockingmechanism 224 to operate the handle from the LOCK state to the UNLOCKEDstate. The rider may manually move handle 220 from the IN position tothe OUT position. The rider may grasp handle 220, lift vehicle 100 offof the ground, and carry vehicle 100 from one location to another.

In some embodiments, handle 220 may include a biasing mechanism, such asa spring, that automatically forces handle 220 to the OUT position whenoperated to the UNLOCKED state. In some embodiments, locking mechanism224 may be configured to selectively lock handle 220 in the OUTposition.

Vehicle 100 may include any suitable apparatus, device, mechanism,and/or structure for preventing water, dirt, or other road debris frombeing transferred by the ground-contacting element to the rider. Forexample, as shown in FIG. 2, vehicle 100 may include first and secondpartial fender portions 228, 232. Portion 228 is shown coupled to firstdeck portion 116, and portion 232 is shown coupled to second deckportion 120. Portion 228 may prevent debris from being transferred fromtire 132 to a portion of the rider positioned on or adjacent deckportion 116, such as when tire 132 is rotated about pitch axis A1 in acounter-clockwise direction. Portion 232 may prevent debris from beingtransferred from tire 132 to a portion of the rider positioned on oradjacent deck portion 120, such as when tire 132 is rotated about pitchaxis A1 in a clockwise direction.

Additionally and/or alternatively, vehicle 100 may include a full fender(not shown). A full fender may be configured to prevent a transfer ofdebris from the ground-contacting element to the rider. A full fenderand/or fender portions 228, 232 may be attached to at least one of deckportions 116, 120 and configured to prevent water traversed by wheel 132from splashing onto the rider. A suitable fender may be attached to oneor both of deck portions 116, 120, and may substantially entirelyseparate wheel 132 from the rider.

Fenders may include a resilient fender. For example, fenders may include(or be) a sheet of substantially flexible or resilient material, such asplastic. A first side of the resilient material may be coupled to deckportion 116 (or board 104 proximate deck portion 116), and a second sideof the resilient material may be coupled to deck portion 120 (or board104 proximate deck portion 120).

As indicated in FIG. 3, the one or more electrical components of vehicle100 may include a power supply 250, a motor controller 254, a riderdetection device 262, a power switch 266, and a charge plug 268. Powersupply 250 may include one or more batteries (e.g., rechargeablebatteries) which may be re-chargeable, such as one or more lithiumbatteries that are relatively light in weight and have a relatively highpower density. In some examples, power supply 250 may include one ormore lithium iron phosphate batteries, one or more lithium polymerbatteries, one or more lithium cobalt batteries, one or more lithiummanganese batteries, or a combination thereof. For example, power supply250 may include sixteen (16) A123 lithium iron phosphate batteries(e.g., size 26650). The batteries of power supply 250 may be arranged ina 16S1P configuration. A microcontroller 269 and/or one or more sensors(or at least one sensor) 270 may be included in or connected to motorcontroller 254 (see FIG. 4). At least one of sensors 270 may beconfigured to measure orientation information (or an orientation) ofboard 104. For example, sensors 270 may be configured to sense movementof board 104 about and/or along the pitch, roll, and/or yaw axes. Themotor may be configured to cause rotation of wheel 132 based on theorientation of board 104. In particular, motor controller 254 may beconfigured to receive orientation information measured by the at leastone sensor of sensors 270 and to cause motor assembly 254 to propel theelectric vehicle based on the orientation information. For example,motor controller 254 may be configured to drive hub motor 144 based onreceived sensed movement of board 104 from sensors 270 viamicrocontroller 269 to propel and/or actively balance vehicle 100.

One or more of the electrical components may be integrated into board104. For example, board 104 may include a first environmental enclosurethat may house power supply 250, and a second environmental enclosurethat may house motor controller 254, and rider detection device 262. Theenvironmental enclosures may protect the one or more electricalcomponents from being damaged, such as by water ingress.

Vehicle 100 may include one or more light assemblies, such as one ormore headlight and/or taillight assemblies. For example, a firstheadlight/taillight assembly (or first light assembly) 272 may bedisposed on or at (and/or connected to) a first end portion of board 104(e.g., at a distal end portion of first deck portion 116), and a secondheadlight/taillight assembly 276 may be disposed on or at (and/orconnected to) a second end portion of board 104 (e.g., at a distal endportion of second deck portion 120). The second end portion of board 104may be opposite the first end portion.

Headlight/taillight assemblies 272, 276 may be configured to reversiblylight vehicle 100. For example, assemblies 272, 276 may indicate thedirection that vehicle 100 is moving by changing color. For example, theheadlight/taillight assemblies may each include one or more high outputred and white LEDs (or other suitable one or more illuminators) 278configured to receive data from microcontroller 269 (and/or a pitchsensor or sensors 270, such as a 3-axis gyro 280—see FIG. 4) andautomatically change color from red to white (or white to red, or afirst color to a second color) based on the direction of movement ofvehicle 100, with white LEDs (or a first color) shining in the directionof motion and red LEDs (or a second color) shining backward (e.g.,opposite the direction of motion). For example, one or more of theheadlight/taillight assemblies (e.g., their respective illuminators) maybe connected to microcontroller 269 via an LED driver, which may beincluded in or coupled to motor controller 254. In some embodiments, theilluminators may include RGB/RGBW LEDs.

Illuminators 278 may be located in and/or protected by skid pads 208,212, as shown in FIG. 3. For example, skid pads 208, 212 may includerespective apertures 286, 290. Illuminators 278 may be disposed in andshine through respective apertures 286, 290. Apertures 286, 290 may bedimensioned to prevent illuminators 278 from contacting the ground. Forexample, apertures 286, 290 may each have a depth that is greater than aheight of illuminators 278. In some embodiments, the illuminators may beseparable from the associated skid pad, so that the skid pads may beremoved without removing the illuminators.

As shown in FIG. 3, first skid pad 208 and a first illuminator 278 aredisposed at a distal end of first deck portion 116, and second skid pad212 and a second illuminator 278 are disposed at a distal end of seconddeck portion 120. Each of skid pads may include an aperture (e.g., skidpad 208 may include aperture 286, and skid pad 212 may include aperture290, as mentioned above) configured to allow light from thecorresponding illuminator to shine through while preventing theilluminator from contacting the ground.

B. Illustrative Control System

FIG. 4 shows a block diagram of various illustrative electricalcomponents of vehicle 10 (or 100), including onboard controls, some orall of which may be included in vehicle 10 (or 100). The electricalcomponents may include a power supply management system 300, a directcurrent to direct current (DC/DC) converter 304, a brushless directcurrent (BLDC) drive logic 306, a power stage 310, one or more 3-axisaccelerometer 314, one or more Hall sensors 318, and/or a motortemperature sensor 322. DC/DC converter 304, BLDC drive logic 306, andpower stage 310 may be included in and/or coupled to motor controller254. In some examples, motor controller 254 may comprise avariable-frequency drive and/or any other suitable drive.Accelerometer(s) 314 may be included in sensors 270.

Active balancing (or self-stabilization) of the electric vehicle may beachieved through the use of a feedback control loop or mechanism. Thefeedback control mechanism may include sensors 270, which may beelectrically coupled to and/or included in motor controller 254.Preferably, the feedback control mechanism includes aProportional-Integral-Derivative (PID) control scheme using one or moregyros (e.g., gyro(s) 280) and one or more accelerometers (e.g.,accelerometer(s) 314). Gyro 280 may be configured to measure a pivotingof the foot deck about its pitch axis. Gyro 280 and accelerometer 314may be collectively configured to estimate (or measure, or sense) a leanangle of board 104, such as an orientation of the foot deck about thepitch, roll and/or yaw axes. In some embodiments, the gyro andaccelerometer 314 may be collectively configured to sense orientationinformation sufficient to estimate the lean angle of frame 104 (or 14)including pivotation about the pitch, roll and/or yaw axes.

As mentioned above, orientation information of board 104 may be measured(or sensed) by gyro 280 and accelerometer 314. The respectivemeasurements (or sense signals) from gyro 280 and accelerometer 314 maybe combined using a complementary or Kalman filter to estimate a leanangle of board 104 (e.g., pivoting of board 104 about the pitch, roll,and/or yaw axes, with pivoting about the pitch axis corresponding to apitch angle (about axle 140 or 36), pivoting about the roll axiscorresponding to a roll or heel-toe angle, and pivoting about the yawaxis corresponding to a side-to-side yaw angle) while filtering out theimpacts of bumps, road texture and disturbances due to steering inputs.For example, gyro 280 and accelerometer 314 may be connected tomicrocontroller 269, which may be configured to correspondingly measuremovement of board 104 about and along the pitch, roll, and/or yaw axes.

Alternatively, the electronic vehicle may include any suitable sensorand feedback control loop configured to self-stabilize a vehicle, suchas a 1-axis gyro configured to measure pivotation of the board about thepitch axis, a 1-axis accelerometer configured to measure a gravityvector, and/or any other suitable feedback control loop, such as aclosed-loop transfer function. Additional accelerometer and gyro axesmay allow improved performance and functionality, such as detecting ifthe board has rolled over on its side or if the rider is making a turn.

The feedback control loop may be configured to drive motor 26, 144 toreduce an angle of board 12, 104 with respect to the ground. Forexample, if a rider were to angle board 12 downward, so that first deckportion 16 was lower' than second deck portion 18 (e.g., if the riderpivoted board 12 counterclockwise (CCW) about axle 34 in FIG. 1), thenthe feedback loop may drive motor 26 to cause CCW rotation of tire 24about the pitch axis (i.e., axle 36) and a clockwise force on board 12.

Thus, motion of the electric vehicle may be achieved by the riderleaning his or her weight toward a selected (e.g., “front”) foot.Similarly, deceleration may be achieved by the rider leaning toward theother (e.g., “back” foot). Regenerative braking can be used to slow thevehicle, as discussed further below. Sustained operation may be achievedin either direction by the rider maintaining their lean toward eitherselected foot.

As indicated in FIG. 4, microcontroller 269 may be configured to send asignal to brushless DC (BLDC) drive logic 306, which may communicateinformation relating to the orientation and motion of board 104. BLDCdrive logic 306 may then interpret the signal and communicate with powerstage 310 to drive motor 144 accordingly. Hall sensors 318 may send asignal to the BLDC drive logic to provide feedback regarding asubstantially instantaneous rotational rate of the rotor of motor 144.Motor temperature sensor 322 may be configured to measure a temperatureof motor 144 and send this measured temperature to logic 306. Logic 306may limit an amount of power supplied to motor 144 based on the measuredtemperature of motor 144 to prevent the motor from overheating.

Certain modifications to the PID loop or other suitable feedback controlloop may be incorporated to improve performance and safety of theelectric vehicle. For example, integral windup may be prevented bylimiting a maximum integrator value, and an exponential function may beapplied to a pitch error angle (e.g., a measured or estimated pitchangle of board 104).

Alternatively or additionally, some embodiments may include neuralnetwork control, fuzzy control, genetic algorithm control,linear-quadratic regulator control, state-dependent Riccati equationcontrol, and/or other control algorithms. In some embodiments, absoluteor relative encoders may be incorporated to provide feedback on motorposition.

In some embodiments, a field-oriented control (FOC) or vector controlsystem may be incorporated into the motor controller (e.g., inmicrocontroller 269, drive logic 306, and/or any other suitableprocessing logic of the motor controller). A suitable FOC system isdepicted in FIG. 5. As described below with respect to FIGS. 5-12, thisFOC system may be configured to divert excess regenerative current,thereby acting as a protective mechanism for the battery.

As mentioned above, during turning, the pitch angle can be modulated bythe heel-toe angle (e.g., pivoting of the board about the roll axis),which may improve performance and prevent a front inside edge of board104 from touching the ground. In some embodiments, the feedback loop maybe configured to increase, decrease, or otherwise modulate therotational rate of the tire if the board is pivoted about the rolland/or yaw axes. This modulation of the rotational rate of the tire mayexert an increased normal force between a portion of the board and therider, and may provide the rider with a sense of “carving” when turning,similar to the feel of carving a snowboard through snow or a surfboardthrough water.

Once the rider has suitably positioned themselves on the board, thecontrol loop may be configured to not activate until the rider moves theboard to a predetermined orientation. For example, an algorithm may beincorporated into the feedback control loop, such that the control loopis not active (e.g., does not drive the motor) until the rider usestheir weight to bring the board up to an approximately level orientation(e.g., 0 degree pitch angle). Once this predetermined orientation isdetected, the feedback control loop may be enabled (or activated) tobalance the electric vehicle and to facilitate a transition of theelectric vehicle from a stationary mode (or configuration, or state, ororientation) to a moving mode (or configuration, or state, ororientation).

With continued reference to FIG. 4, the various electrical componentsmay be configured to manage power supply 250. For example, power supplymanagement system 300 may be a battery management system configured toprotect batteries of power supply 250 from being overcharged,over-discharged, and/or short-circuited. System 300 may monitor batteryhealth, may monitor a state of charge in power supply 250, and/or mayincrease the safety of the vehicle. Power supply management system 300may be connected between a charge plug 268 of vehicle 10 and powersupply 250. The rider (or other user) may couple a charger to plug 268and re-charge power supply 250 via system 300.

In operation, power switch 266 may be activated (e.g., by the rider).Activation of switch 266 may send a power-on signal to converter 304. Inresponse to the power-on signal, converter 304 may convert directcurrent from a first voltage level provided by power supply 250 to oneor more other voltage levels. The other voltage levels may be differentthan the first voltage level. Converter 304 may be connected to theother electrical components via one or more electrical connections toprovide these electrical components with suitable voltages.

Converter 304 (or other suitable circuitry) may transmit the power-onsignal to microcontroller 269. In response to the power-on signal,microcontroller may initialize sensors 270, and rider detection device262.

The electric vehicle may include one or more safety mechanisms, such aspower switch 266 and/or rider detection device 262 to ensure that therider is on the board before engaging the feedback control loop. In someembodiments, rider detection device 262 may be configured to determineif the rider's feet are disposed on the foot deck, and to send a signalcausing motor 144 to enter an active state when the rider's feet aredetermined to be disposed on the foot deck.

Rider detection device 262 may include any suitable mechanism,structure, or apparatus for determining whether the rider is on theelectric vehicle. For example, device 262 may include one or moremechanical buttons, one or more capacitive sensors, one or moreinductive sensors, one or more optical switches, one or moreforce-resistive sensors, and/or one or more strain gauges. Riderdetection device 262 may be located on or under either or both of firstand second deck portions 16, 18 or 116, 120 (see FIGS. 1-2). In someexamples, the one or more mechanical buttons or other devices may bepressed directly (e.g., if on the deck portions), or indirectly (e.g.,if under the deck portions), to sense whether the rider is on board 104.In some examples, the one or more capacitive sensors and/or the one ormore inductive sensors may be located on or near a surface of either orboth of the deck portions, and may correspondingly detect whether therider is on the board via a change in capacitance or a change ininductance. In some examples, the one or more optical switches may belocated on or near the surface of either or both of the deck portions.The one or more optical switches may detect whether the rider is on theboard based on an optical signal. In some examples, the one or morestrain gauges may be configured to measure board or axle flex impartedby the rider's feet to detect whether the rider is on the board. In someembodiments, device 262 may include a hand-held “dead-man” switch.

If device 262 detects that the rider is suitably positioned on theelectric vehicle, then device 262 may send a rider-present signal tomicrocontroller 269. The rider-present signal may be the signal causingmotor 26, 144 to enter the active state. In response to therider-present signal (and/or the board being moved to the levelorientation), microcontroller 269 may activate the feedback control loopfor driving motor 144. For example, in response to the rider-presentsignal, microcontroller 269 may send board orientation information (ormeasurement data) from sensors 270 to logic 306 for powering motor 26,144 via power stage 310.

In some embodiments, if device 262 detects that the rider is no longersuitably positioned or present on the electric vehicle, device 262 maysend a rider-not-present signal to microcontroller 269. In response tothe rider-not-present signal, circuitry of vehicle 10 (e.g.,microcontroller 269, logic 306, and/or power stage 310) may beconfigured to reduce a rotational rate of the rotor relative to thestator to bring vehicle 10 to a stop. For example, the electric coils ofthe rotor may be selectively powered to reduce the rotational rate ofthe rotor. In some embodiments, in response to the rider-not-presentsignal, the circuitry may be configured to energize the electric coilswith a relatively strong and/or substantially continuously constantvoltage, to lock the rotor relative to the stator, to prevent the rotorfrom rotating relative to the stator, and/or to bring the rotor to asudden stop.

In some embodiments, the vehicle may be configured to actively drivemotor 26, 144 even though the rider may not be present on the vehicle(e.g., temporarily), which may allow the rider to perform varioustricks. For example, device 262 may be configured to delay sending therider-not-present signal to the microcontroller for a predeterminedduration of time, and/or the microcontroller may be configured to delaysending the signal to logic 306 to cut power to the motor for apredetermined duration of time.

C. Illustrative Motor Controller Using Field-Oriented Control

FIGS. 5-13 relate to a field-oriented control (FOC) system and algorithmconfigured to manage stator voltages to run a BLDC motor of a vehicle,such as vehicles 10, 100 described in Section A. The FOC systemdescribed below may be part of or coupled to a motor controller, such asmotor controller 254 described in Section B.

In general, FOC is used to ensure maximum torque is applied for a givenamount of current, by maximizing the net current vector in a direction90-degrees with respect to the rotor flux. This is accomplished bycontrolling two orthogonal component vectors: a direct current (i_(d))pointed along the rotor flux axis and a quadrature current (i_(q))pointed 90 degrees from the direct current vector. As mentioned above,the direct current may be referred to as the flux current.

The orientations of the vectors mean that maximizing the quadraturecurrent and minimizing the direct current would cause the most efficientoverall net current vector (i.e., at 90 degrees from the rotor flux). Asdescribed in the Overview above, motor controllers of the presentdisclosure are further configured to operate the motor inefficientlywhen the battery is in danger of an over-voltage condition. To do this,the controller selectively causes the direct (flux) current to be raisedwhen CEMF is greater than battery voltage, thereby both weakening therotor flux (and CEMF) and dumping excess current along anon-torque-inducing vector. FIG. 5 is a block diagram of an illustrativeFOC system 500 (also referred to as a

FOC scheme or FOC platform) suitable for use with aspects of the presentdisclosure. FIGS. 6-11 depict the various vector current frameworksdiscussed below. FIGS. 12 and 13 depict steps of illustrative methods oralgorithms (700, 800) used by FOC system 500.

With reference to FIGS. 5 and 6-7, each of the three phase currents ofthe motor may be controlled by controlling applied stator voltages,namely V_(U), V_(V), and V_(W). To this end, stator currents (i_(U),i_(V), and i_(W)) are measured, usually by measuring two of the currentsand calculating the third. These three currents comprise vectors thatcan be added together to determine the resulting net current vector.Controlling the three currents therefore controls the net currentvector, and a relationship between the net current vector and the rotorflux vector determines how much torque is experienced by the rotor.Specifically, maximum motor torque is achieved when the net statorcurrent vector is ninety degrees from the rotor flux.

Controllers of this type are generally configured to maintain the netcurrent vector at 90 degrees from the rotor flux, and to control theamount of motor torque by regulating the amplitude of the net currentvector. Accordingly, the controller (e.g., a position and speedestimator module 520) measures the rotor position (e.g., using Hallsensors, an encoder, a resolver, a sensorless approach, etc.), whichdetermines the rotor flux position, and then the controller adjusts thenet current vector to be pointed 90 degrees from the rotor fluxposition. Rather than directly determining which values of the threestator voltages to apply, which is complex and requires additionalcomponents, system 500 first simplifies the net current vector bymathematically converting it to a two-axis framework 530 (see FIG. 8)(axes α and β) using the Clarke Transformation 540 (known in the art andalso referred to as the Forward Clarke transformation). Thistransformation results in expression of the net current vector as itstwo components in the α, β reference frame: i_(α) and i_(β) (see FIG.9). These component vectors could theoretically be used to determine thedesired V_(α) and V_(β), which may be converted back to a three-axissystem (e.g., three-axis system 550, depicted in FIG. 6) to drive themotor. However, further simplification is possible and desired, becausethe α and β axes form a stationary frame of reference while the netcurrent vector is rotating through space. That means i_(α) and i_(β)vary over time (e.g., sinusoidally), as shown in FIG. 9.

Accordingly, i_(α) and i_(β) are transformed to a two-dimensionalrotating frame of reference 560 (see FIG. 10) that is aligned andsynchronized with the rotating rotor. In this reference frame, a first(direct) axis, d, is oriented along (i.e., directly aligned with) therotor flux vector, and a second (quadrature) axis, q, is oriented at 90degrees from the first axis. Note that the q axis is the direction inwhich the maximum torque is generated. A benefit of the rotatingreference frame is that the axes are stationary relative to the rotor,and the component vectors will now be generally constant orslow-changing (i.e., DC currents), as shown in FIG. 11. To accomplishthis simplification, i_(α) and i_(β) are converted into i_(d) and i_(q),using the Park Transformation 570 (known in the art, and also referredto as the Forward Park Transformation).

At this point, i_(d) and i_(q) can be handled independently tomanipulate the net current vector. It should be clear that any non-zeromagnitude of i_(d) will alter the net current vector from the quadrature(i.e., maximum-torque) direction. Accordingly, during normal operation,i_(d) is usually commanded to be zero while i_(q) is controlled inaccordance with desired torque. With continuing reference to FIG. 5, themeasured i_(d) and i_(q) are compared to the commanded i_(d) and i_(q),and respective proportional-integral (PI) controllers PI_(d) and PI_(q)are used to determine the corresponding V_(d) and V_(q). These voltagevalues are then passed through modules (labeled PARK⁻¹ and 2φ→3φ) thatperform an Inverse Park Transformation and an Inverse ClarkeTransformation to convert them back to the α, β stationary referenceframe and finally to the three phase values needed for applying statorvoltages V_(U), V_(V), and V_(W).

The question remains what the commanded i_(d) and i_(q) should be. Asdepicted in FIG. 5, system 500 includes an intelligent regenerationcontroller module 510 that takes the commanded flux (direct) currenti_(d), the commanded torque (quadrature) current i_(q), and the batterybus voltage, and determines the proper desired flux current to protectthe battery from an over-voltage condition.

Commanded torque will depend on the desired speed and direction of themotor, as commanded by the user/rider. For example, in vehicles 10, 100,torque commands will be based on the tilt angle or orientation of theboard, which is generally caused by user action. The flux command, onthe other hand, depends on how much the system needs to weaken theoverall flux, reduce the torque, and/or redirect excess current.

Turning now to FIGS. 12 and 13, methods are depicted suitable forexecution by the motor controller. For example, intelligent regenerationcontroller 510 of system 500 may utilize one or both of these methods.Aspects of system 500 and/or vehicles 10, 100 may be utilized in themethod steps described below. Where appropriate, reference may be madeto components and systems that may be used in carrying out each step.These references are for illustration, and are not intended to limit thepossible ways of carrying out any particular step of the method.

FIG. 12 is a flowchart illustrating steps performed in a method 700, andmay not recite the complete process or all steps of the method. Althoughvarious steps of method 700 are described below and depicted in FIG. 12,the steps need not necessarily all be performed, and in some cases maybe performed simultaneously or in a different order than the ordershown.

In method 700, the system (e.g., system 500) monitors a battery busvoltage of the battery that is coupled to the motor in question (block702). Although a single battery is referenced here, any number orcombination of batteries or battery cells may be present. If batteryvoltage becomes greater than a selected overvoltage threshold (block704), which may be a percentage of a fully-charged voltage rating (e.g.,100%, 110%), it may be assumed that power is being generated by themotor, e.g., in a regenerative braking or other situation where the CEMFis greater than the battery voltage. In response, the system mayautomatically increase the flux current (direct current i_(d) describedabove). This increase in flux current acts both to divert excess currentalong a non-torque-inducing vector (i.e., “wasting” the excess current)and to weaken the motor flux. Weakening the motor flux results in lowerCEMF and less excess current being generated in the first place. Whilethe over-voltage condition is in effect, the flux current increase maybe automatically continued until a selected maximum flux weakening valueis reached (block 706).

Conversely, if battery bus voltage is determined to be less than theover-voltage limit (or threshold) (block 708), then the flux current isautomatically decreased or reduced. This is done to prevent inefficientoperation in normal operating conditions. In other words, in thissituation reducing the direct current reduces inefficiency of the motor.As long as the over-voltage condition is absent, the flux currentreduction may be automatically continued until a selected minimum fluxweakening value (e.g., zero amps) is reached (block 710).

FIG. 13 is a flowchart illustrating steps performed in a method 800, andmay not recite the complete process or all steps of the method. Althoughvarious steps of method 800 are described below and depicted in FIG. 13,the steps need not necessarily all be performed, and in some cases maybe performed simultaneously or in a different order than the ordershown.

Step 802 of algorithm 800 includes comparing the bus voltage of thepower supply (e.g., the battery) to an overvoltage limit or threshold.If the bus voltage is below the limit, step 804 includes reducing a fluxcurrent setpoint, unless the setpoint is already at zero. If the busvoltage is at or above the limit, step 806 includes increasing the fluxcurrent setpoint, unless the setpoint is already at a selected maximumallowable value.

Step 808 includes comparing the flux current setpoint to the commandedflux current. Whichever value is higher is then passed on to thecontroller as the desired flux current. In other words, if commandedflux exceeds the flux setpoint, desired flux will be set to thecommanded flux. If commanded flux is less than the flux setpoint,desired flux will be set to the higher setpoint. This results in araising of the commanded flux in situations where an overvoltagesituation is in progress. Increases and decreases of the flux setpointmay be iterative in nature. In some examples, the increases anddecreases happen in substantially equal jumps. In some examples, quantumincreases are larger than quantum decreases, such that the redirectionof current to the flux weakening vector will respond faster than thereverse operation.

After completing step 808, the algorithm loops back to step 802 tocontinue the control method. In some examples, this looping issubstantially continuous. In some examples, each iteration of the loopis triggered by an event, e.g., in the case of an interrupt handlerkicked off by an interrupt request (IRQ).

D. Illustrative Combinations and Additional Examples

This section describes additional aspects and features of controlsystems having over-voltage prevention features in regenerative energysituations, presented without limitation as a series of paragraphs, someor all of which may be alphanumerically designated for clarity andefficiency. Each of these paragraphs can be combined with one or moreother paragraphs, and/or with disclosure from elsewhere in thisapplication, in any suitable manner. Some of the paragraphs belowexpressly refer to and further limit other paragraphs, providing withoutlimitation examples of some of the suitable combinations.

C0. An electric vehicle with one or more wheels driven by a permanentmagnet motor, wherein the vehicle uses said motor for braking,comprising a control system in which a novel technique is implemented todispose of the excess power when the vehicle is regenerating power toprevent over-voltage damage to the system. The novel technique disposesof energy by intentionally inefficiently operating the motor when thebatteries are fully charged and cannot safely absorb more regeneratedpower.

C1. The technique of CO may be used to prevent exceeding the batterycells' maximum charge rate in hard braking/downhill scenarios.

D0. A self-balancing vehicle having a motor that provides braking torquewhile descending downhill or stopping, having a control system thatresults in reduced risk of damaging the system or suddenly shutting downwhen the battery is near full charge. This allows the self-balancingvehicle to drive downhill at a faster speed and stop quickly with lessrisk of system damage and less risk of rider injury.

E0. In some embodiments, a permanent magnet motor (BLDC) controltechnique is provided that drives the motor in field-oriented control(FOC) allowing the flux and torque currents to be manipulatedindependently. The motor flux can be controlled in such a way as toreduce the back-EMF voltage, which reduces regenerated current. Inaddition to reducing the back-EMF, this process also wastes excessenergy in the process by flowing current in the flux region of themotor, further disposing of the regenerated power.

F0. Control techniques described herein may drive the permanent magnetmotor in such a way as to continue to have braking torque while reducingor eliminating the regenerated power, allowing the rider to continuedownhill at a faster speed and/or stop quickly without raising thesystem voltage and damaging the control system and battery pack.

G0. Aspects of the present disclosure may also be relevant to systemswith mechanical brakes (electric bicycles, motorcycles, cars, etc.) butwhich seek to use regenerative braking even when at a high state ofcharge.

H0. A control system for an electric vehicle, the control systemcomprising:

a power supply;

an electric motor coupled to the power supply; and

a motor controller having a field-oriented control (FOC) schemeconfigured to control the electric motor by manipulating a directcurrent aligned with a rotating rotor flux angle and a quadraturecurrent defined at ninety degrees from the rotating rotor flux angle,wherein manipulation of the direct current is independent ofmanipulation of the quadrature current, and the motor controllerincludes processing logic configured to:

-   -   determine whether a counter electromotive force (CEMF) of the        electric motor exceeds a voltage of the power supply by        comparing a bus voltage of the power supply to a voltage        threshold; and    -   in response to the bus voltage being greater than the voltage        threshold, weakening a motor flux of the electric motor and        reducing the CEMF by automatically increasing the direct        current.

H1. The control system of H0, wherein the processing logic of the motorcontroller is further configured to:

-   -   while the bus voltage is greater than the voltage threshold,        automatically continue to increase the direct current of the        motor; and    -   in response to the direct current reaching a direct current        threshold, automatically stop increasing the direct current.

H2. The control system of any one of paragraphs H0 through H1, whereinautomatically increasing the direct current comprises:

increasing a flux setpoint of the motor controller by a selected amount;

comparing an existing flux command to the flux setpoint; and

adjusting direct current to a higher of the existing flux command andthe flux setpoint.

H3. The control system of any one of paragraphs H0 through H2, whereinthe processing logic of the motor controller is further configured to:in response to the bus voltage being less than the voltage threshold andthe direct current being greater than zero, reducing inefficiency of themotor by automatically reducing the direct current.

H4. The control system of H3, wherein automatically reducing the directcurrent comprises:

decreasing a flux setpoint of the motor controller by a selected amount;

comparing an existing flux command to the flux setpoint; and

adjusting direct current to a higher of the existing flux command andthe flux setpoint.

H5. The control system of any one of paragraphs H0 through H4, whereinthe power supply comprises a lithium ion battery.

H6. The control system of claim 1, wherein the electric motor comprisesa hub motor configured to rotate a wheel of a vehicle.

Note: Paragraph labels beginning with the letter “I” are intentionallyskipped, to avoid confusion with the number “1”.

J0. An electric vehicle comprising:

one or more wheels;

an electric hub motor coupled to a power supply and configured to drivethe one or more wheels;

a motor controller having a field-oriented control (FOC) schemeconfigured to control the electric hub motor by manipulating a directcurrent aligned with a rotating rotor flux angle and a quadraturecurrent defined at ninety degrees from the rotating rotor flux angle,wherein manipulation of the direct current is independent ofmanipulation of the quadrature current, and the motor controllerincludes processing logic configured to:

-   -   determine whether a counter electromotive force (CEMF) of the        electric motor exceeds a voltage of the power supply by        comparing a bus voltage of the power supply to a voltage        threshold; and    -   in response to the bus voltage being greater than the voltage        threshold, weakening a motor flux of the electric motor and        reducing the CEMF by automatically increasing the direct        current.

J1. The vehicle of J0, wherein the vehicle has exactly one wheel.

J2. The vehicle of J1, wherein the vehicle comprises a self-balancingelectric skateboard, the skateboard comprising:

a board including first and second deck portions each configured toreceive a left or right foot of a rider oriented generally perpendicularto a direction of travel of the board;

a wheel assembly including the exactly one wheel disposed between andextending above the first and second deck portions, wherein the electrichub motor is configured to rotate the wheel around an axle to propel theskateboard; and

at least one sensor configured to measure orientation information of theboard;

wherein the motor controller is further configured to receiveorientation information measured by the sensor and to cause the hubmotor to propel the skateboard based on the orientation information.

J3. The vehicle of any one of paragraphs J0 through J2, wherein theprocessing logic of the motor controller is further configured to:

while the bus voltage is greater than the voltage threshold,automatically continue to increase the direct current of the motor; and

in response to the direct current reaching a direct current threshold,automatically stop increasing the direct current.

J4. The vehicle of any one of paragraphs J0 through J3, whereinautomatically increasing the direct current comprises:

increasing a flux setpoint of the motor controller by a selected amount;

comparing an existing flux command to the flux setpoint; and

adjusting direct current to the higher of the existing flux command andthe flux setpoint.

J5. The vehicle of any one of paragraphs J0 through J4, wherein theprocessing logic of the motor controller is further configured to: inresponse to the bus voltage being less than the voltage threshold andthe direct current being greater than zero, reducing inefficiency of themotor by automatically reducing the direct current.

J6. The vehicle of J5, wherein automatically reducing the direct currentcomprises:

decreasing a flux setpoint of the motor controller by a selected amount;

comparing an existing flux command to the flux setpoint; and

adjusting direct current to a higher of the existing flux command andthe flux setpoint.

K0. A method for preventing damage to a power supply of an electricvehicle during regenerative braking, the method comprising:

controlling an electric motor using a motor controller having afield-oriented control (FOC) scheme configured to control the electricmotor by manipulating a direct current aligned with a rotating rotorflux angle and a quadrature current defined at ninety degrees from therotating rotor flux angle, wherein manipulation of the direct current isindependent of manipulation of the quadrature current;

using processing logic of the motor controller to determine whether acounter electromotive force (CEMF) of the electric motor exceeds avoltage of the power supply; and

in response to the CEMF of the electric motor exceeding the voltage ofthe power supply, weakening a motor flux of the electric motor andreducing the CEMF by automatically increasing the direct current.

K1. The method of K0, wherein determining whether the CEMF of theelectric motor exceeds the voltage of the power supply comprisescomparing a bus voltage of the power supply to a voltage threshold.

K2. The method of K0 or K1, further comprising: while the CEMF of theelectric motor exceeds the voltage of the power supply, automaticallycontinuing to increase the direct current of the motor until the directcurrent reaches a direct current threshold.

K3. The method of any one of paragraphs K0 through K2, whereinautomatically increasing the direct current comprises:

increasing a flux setpoint of the motor controller by a selected amount;

comparing an existing flux command to the flux setpoint; and

adjusting direct current to a higher of the existing flux command andthe flux setpoint.

K4. The method of any one of paragraphs K0 through K3, furthercomprising: in response to the CEMF of the electric motor being belowthe voltage of the power supply and the direct current being greaterthan zero, reducing inefficiency of the motor by automatically reducingthe direct current.

K5. The method K4, wherein automatically reducing the direct currentcomprises:

decreasing a flux setpoint of the motor controller by a selected amount;

comparing an existing flux command to the flux setpoint; and

adjusting direct current to a higher of the existing flux command andthe flux setpoint.

CONCLUSION

The disclosure set forth above may encompass multiple distinct exampleswith independent utility. Although each of these has been disclosed inits preferred form(s), the specific embodiments thereof as disclosed andillustrated herein are not to be considered in a limiting sense, becausenumerous variations are possible. To the extent that section headingsare used within this disclosure, such headings are for organizationalpurposes only. The subject matter of the disclosure includes all noveland nonobvious combinations and subcombinations of the various elements,features, functions, and/or properties disclosed herein. The followingclaims particularly point out certain combinations and subcombinationsregarded as novel and nonobvious. Other combinations and subcombinationsof features, functions, elements, and/or properties may be claimed inapplications claiming priority from this or a related application. Suchclaims, whether broader, narrower, equal, or different in scope to theoriginal claims, also are regarded as included within the subject matterof the present disclosure.

What is claimed is:
 1. A control system for an electric vehicle, thecontrol system comprising: a power supply; an electric motor coupled tothe power supply; and a motor controller having a field-oriented control(FOC) scheme configured to control the electric motor by manipulating adirect current aligned with a rotating rotor flux angle and a quadraturecurrent defined at ninety degrees from the rotating rotor flux angle,wherein manipulation of the direct current is independent ofmanipulation of the quadrature current; wherein the motor controllerincludes processing logic configured to automatically weaken a motorflux of the electric motor when a bus voltage of the power supplyexceeds a voltage threshold.
 2. The control system of claim 1, whereinthe processing logic of the motor controller is configured to weaken themotor flux of the electric motor by automatically increasing the directcurrent.
 3. The control system of claim 2, wherein the processing logicof the motor controller is further configured to: while the bus voltageis greater than the voltage threshold, automatically continue toincrease the direct current of the motor; and in response to the directcurrent reaching a direct current threshold, automatically stopincreasing the direct current.
 4. The control system of claim 2, whereinautomatically increasing the direct current comprises: increasing a fluxsetpoint of the motor controller by a selected amount; comparing anexisting flux command to the flux setpoint; and adjusting the directcurrent to a higher of the existing flux command and the flux setpoint.5. The control system of claim 1, wherein the processing logic of themotor controller is further configured to: in response to the busvoltage being less than the voltage threshold and the direct currentbeing greater than zero, reducing inefficiency of the motor byautomatically reducing the direct current.
 6. The control system ofclaim 5, wherein automatically reducing the direct current comprises:decreasing a flux setpoint of the motor controller by a selected amount;comparing an existing flux command to the flux setpoint; and adjustingthe direct current to a higher of the existing flux command and the fluxsetpoint.
 7. The control system of claim 1, wherein the electric motorcomprises a hub motor configured to rotate a wheel of a vehicle.
 8. Anelectric vehicle comprising: one or more wheels; an electric hub motorcoupled to a power supply and configured to drive the one or morewheels; and a motor controller having a field-oriented control (FOC)scheme configured to control the electric hub motor by manipulating adirect current aligned with a rotating rotor flux angle and a quadraturecurrent defined at ninety degrees from the rotating rotor flux angle,wherein manipulation of the direct current is independent ofmanipulation of the quadrature current; wherein the motor controllerincludes processing logic configured to automatically weaken a motorflux of the electric motor and reduce a counter electromotive force(CEMF) of the electric motor when a bus voltage of the power supplyexceeds a voltage threshold.
 9. The vehicle of claim 8, wherein thevehicle comprises a self-balancing electric skateboard, the skateboardcomprising: a board including first and second deck portions eachconfigured to receive a left or right foot of a rider oriented generallyperpendicular to a direction of travel of the board; a wheel assemblyincluding exactly one wheel disposed between and extending above thefirst and second deck portions, wherein the electric hub motor isconfigured to rotate the wheel around an axle to propel the skateboard;and at least one sensor configured to measure orientation information ofthe board; wherein the motor controller is further configured to receiveorientation information measured by the sensor and to cause the hubmotor to propel the skateboard based on the orientation information. 10.The electric vehicle of claim 8, wherein weakening the motor flux of theelectric motor and reducing the CEMF of the electric motor includesautomatically increasing the direct current.
 11. The vehicle of claim10, wherein the processing logic of the motor controller is furtherconfigured to: while the bus voltage is greater than the voltagethreshold, automatically continue to increase the direct current of themotor; and in response to the direct current reaching a direct currentthreshold, automatically stop increasing the direct current.
 12. Thevehicle of claim 10, wherein automatically increasing the direct currentcomprises: increasing a flux setpoint of the motor controller by aselected amount; comparing an existing flux command to the fluxsetpoint; and adjusting the direct current to the higher of the existingflux command and the flux setpoint.
 13. The vehicle of claim 8, whereinthe processing logic of the motor controller is further configured to:in response to the bus voltage being less than the voltage threshold andthe direct current being greater than zero, reducing inefficiency of themotor by automatically reducing the direct current.
 14. The vehicle ofclaim 13, wherein automatically reducing the direct current comprises:decreasing a flux setpoint of the motor controller by a selected amount;comparing an existing flux command to the flux setpoint; and adjustingdirect current to a higher of the existing flux command and the fluxsetpoint.
 15. A method for preventing damage to a power supply of anelectric vehicle during regenerative braking, the method comprising:controlling an electric motor using a motor controller having afield-oriented control (FOC) scheme configured to control the electricmotor by manipulating a direct current aligned with a rotating rotorflux angle and a quadrature current defined at ninety degrees from therotating rotor flux angle, wherein manipulation of the direct current isindependent of manipulation of the quadrature current; and in responseto a counter electromotive force (CEMF) of the electric motor exceedinga voltage of the power supply, weakening a motor flux of the electricmotor and reducing the CEMF.
 16. The method of claim 15, whereinweakening the motor flux of the electric motor and reducing the CEMFcomprises automatically increasing the direct current.
 17. The method ofclaim 16, further comprising: while the CEMF of the electric motorexceeds the voltage of the power supply, automatically continuing toincrease the direct current of the motor until the direct currentreaches a direct current threshold.
 18. The method of claim 16, whereindetermining whether the CEMF of the electric motor exceeds the voltageof the power supply comprises comparing a bus voltage of the powersupply to a voltage threshold.
 19. The method of claim 16, whereinautomatically increasing the direct current comprises: increasing a fluxsetpoint of the motor controller by a selected amount; comparing anexisting flux command to the flux setpoint; and adjusting the directcurrent to a higher of the existing flux command and the flux setpoint.20. The method of claim 15, further comprising: in response to the CEMFof the electric motor being below the voltage of the power supply andthe direct current being greater than zero, reducing inefficiency of themotor by automatically reducing the direct current.